If I send a message using Yahoo! Messenger, can the receiver track down the PC or device it was sent from?
That was possible in the past but Yahoo secured all the sending and receiving protocols and nowadays it's impossible to tell where the message is coming from regarding IP address, operating system used, etc.
it is possible to view the whole message including header,sender and IPs in yahoo. alternatively you can pick up your mail through another app - thunderbird for instance - and be outside of yahoo
it is possible to view your ip address .